/*
 * Copyright (C) 2020 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.android.tools.idea.uibuilder.scene;

/**
 * An implementation of session clock that provides a real time passed since the time of its construction.
 */
public class RealTimeSessionClock implements SessionClock {
  private static final long INVALID_TIME = -1;
  private long myStartTimeNanos = System.nanoTime();
  /**
   * Time in nanos when the pause was set if in pause or INVALID_TIME otherwise.
   */
  private long myPauseTimeNanos = INVALID_TIME;

  @Override
  public synchronized long getTimeNanos() {
    if (myPauseTimeNanos != INVALID_TIME) {
      return myPauseTimeNanos - myStartTimeNanos;
    }
    return System.nanoTime() - myStartTimeNanos;
  }

  @Override
  public synchronized void pause() {
    if (myPauseTimeNanos == INVALID_TIME) {
      myPauseTimeNanos = System.nanoTime();
    }
  }

  @Override
  public synchronized void resume() {
    if (myPauseTimeNanos == INVALID_TIME) {
      return;
    }
    // Shift the start time by the time spent in pause
    myStartTimeNanos += System.nanoTime() - myPauseTimeNanos;
    myPauseTimeNanos = INVALID_TIME;
  }
}
